In cosmology, the cosmic microwave background radiation CMB (also CMBR, CBR, MBR, and relic radiation) is a form of electromagnetic radiation filling the universe. It has a thermal black body spectrum at a temperature of 2.725 K, thus the spectrum peaks in the microwave range frequency of 160.2 GHz, corresponding to a 1.9mm wavelength. The CMB's discovery in 1964 by astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s.
Measurements of cosmic background radiation are critical to cosmology, since any proposed model of the universe must explain this radiation as we observe it. Although the general feature of a black-body radiation spectrum could potentially be produced by many processes, the spectrum also contains small anisotropies, or irregularities, which vary with the size of the region examined. They have been measured in detail, and match to within experimental error that would be expected if small thermal fluctuations had expanded to the size of the observable space we can detect today. As a result, most cosmologists consider this radiation to be the best evidence for the Big Bang model of the universe. See the plot of power spectrum of the cosmic microwave background radiation temperature anisotropy in terms of the angular scale below for details.
